Method for quantitative determination of the suitability of crystals for optical components exposed to high energy densities, crystals graded in this way and uses thereof

Abstract

A method is described for quantitative determination of suitability of an optical material, especially alkali halide and alkaline earth halide single crystals, for optical components exposed to high energy densities, especially of pulsed laser light at wavelengths under 250 nm. In this procedure radiation-dependent transmission of the optical material is determined at ultraviolet wavelengths by fluorescence measurements for fluorescence induced by ultraviolet radiation at these ultraviolet wavelengths. This is accomplished by a method including determining an induced fluorescence maximum of a non-linear absorption process, measuring a slope (|dT/dH|) of a functional relationship representing the dependence of the radiation-dependent transmission on fluence (H) for the induced, fluorescence and determining radiation-dependent transmissions from this slope for particular fluence values.

1. An optical material for an optical component exposed to a high energy density having a radiation-dependent transmission, wherein said radiation-dependent transmission has a rate of change with respect to fluence for incident ultraviolet radiation at ultraviolet wavelengths under 250 nm of at most 0.2% per mJ/cm 2 . 
     
     
       2. The optical material as defined in  claim 1 , selected from the group consisting of CaF 2 , BaF 2 , SrF 2 , LiF, KF, NaF and KMgF 3 . 
     
     
       3. An optical component through which ultraviolet radiation at a wavelength less than 250 nm passes at a high energy density, said optical component consisting of an optical material having a radiation-dependent transmission, wherein said radiation-dependent transmission has a rate of change with respect to fluence for an incident ultraviolet radiation at a wavelength of under 250 nm of at most 0.2% per mJ/cm 2 . 
     
     
       4. The optical component as defined in  claim 3 , consisting of a lens, prism, light conducting rod or an optical window for DUV photolithography, steppers, excimer lasers, wafers, computer chips and integrated circuits as well as electronic equipment containing said computer chips and said integrated circuits. 
     
     
       5. The optical material as defined in  claim 1 , wherein said rate of change of said radiation-dependent transmission with respect to said fluence is obtained by measuring fluorescence induced by said ultraviolet radiation at said ultraviolet wavelengths.